Implantable cardiac stimulation devices are well known in the art. Such devices may include, for example, implantable cardiac pacemakers and defibrillators. The devices are generally implanted in a pectoral region of the chest beneath the skin of a patient within what is known as a subcutaneous pocket. The implantable devices generally function in association with one or more electrode carrying leads which are implanted within the heart. The electrodes are usually positioned within the right side of the heart, either within the right ventricle or right atrium, or both, for making electrical contact with their respective heart chamber. Conductors within the leads and a proximal connector carried by the leads couple the electrodes to the device to enable the device to sense cardiac electrical activity and deliver the desired therapy.
Traditionally, therapy delivery had been limited to the venous or right side of the heart. The reason for this is that implanted electrodes can cause blood clot formation in some patients. If a blood clot were released arterially from the left heart, as for example the left ventricle, it could pass directly to the brain potentially resulting in a paralyzing or fatal stroke. However, a blood clot released from the right heart, as from the right ventricle, would pass into the lungs where the filtering action of the lungs would prevent a fatal or debilitating embolism in the brain.
Recently, new lead structures and methods have been proposed and even practiced for delivering cardiac rhythm management therapy to the left heart. These lead structures and methods avoid direct electrode placement within the left atrium and left ventricle of the heart by lead implantation within the coronary sinus region of the heart. As used herein, the phrase “coronary sinus region” refers to the venous vasculature of the left ventricle, including any portions of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.
It has been demonstrated that electrodes placed in the coronary sinus region of the heart may be used for left atrial pacing, left ventricular pacing, or cardioversion and defibrillation. These advancements enable implantable cardiac stimulation devices to address the needs of a patient population with left ventricular dysfunction and/or congestive heart failure which would benefit from left heart side pacing, either alone or in conjunction with right heart side pacing (bi-chamber pacing), and/or defibrillation.
Notwithstanding the advancements in left heart therapy using leads/electrodes implanted in the coronary sinus region of the heart, it would still be very desirable to alternatively be able to place a lead/electrode in the left ventricular cavity. This would enable the electrode(s) to contact the left ventricular blood pool. Such blood pool contact would lower left heart pacing thresholds and hence extend device life by requiring lower pacing outputs. It would also enable more localized sensing of left heart activity. This which would lead to better coordination of right heart side and left heart side therapy due to increased specificity in left heart activity detection.
As previously mentioned, direct access to the left heart, such as the left ventricle, has been limited due to the potential of clot formation around implanted leads and electrodes. The present invention addresses this issue by providing an implantable cardiac stimulation system capable of delivering stimulation pulses to an electrode implanted in the blood pool of the left ventricle while preventing clot formation which may be otherwise potentially occasioned by such an arrangement.